1. Field of the Invention
The invention relates to a displacement machine for compressible mediums with several spiral-shaped conveying spaces, which are disposed in a stationary housing, and to a displacement body which is assigned to the conveying spaces and which is driven eccentrically relative to the housing so that during service each of its points effects a circular movement defined by the circumferential walls of the displacement chamber. An eccentric disk, on which the rotor is mounted by means of an oil-lubricated mounting, is disposed on the drive shaft.
2. State of the Art
Displacement machines of the spiral design are known, for example, from the DE-C-26 03 462. A compressor built according to this principle provides an almost pulsation-free conveying of the gaseous working medium which consists of, for example, air or at mixture of air and fuel. It could, therefore, also be used advantageously for the purpose of charging internal combustion engines. When such a compressor is operating, several crescent-shaped working spaces, which move from the inlet through the displacement chamber to the outlet, are enveloped along the displacement chamber between the spiral-shaped displacement body and the two circumferential walls of the displacement chamber, resulting in their volumes continuously decreasing and the pressure of the working medium being correspondingly increased.
A machine of the aforementioned kind is known from EP 0 354 342. In this machine and, moreover, in all known spiral compressors, in which for the translatory guide of the rotor a guide shaft that runs conformally with the drive shaft is provided, the drive shaft is mounted in roller bearings. This is especially obvious in the displacement machine according to the EP 0 354 342, in which the drive shaft is mounted in two ball bearings and the eccentric collar disposed on the drive shaft is mounted by way of a needle bearing.
The kind of bracing or mounting of the rotor is relatively expensive, since for space reasons a needle bearing without the inner race is used. This requires, however, that the rollway on the eccentric collar must be hardened, a feature that in turn limits the choice of an optimal method for producing the eccentric shaft. An optimal process is the casting process in which spherulitic graphite cast iron is used. Spherulitic graphite cast iron can be hardened; in the meantime the strength that is necessary for a highly stressed roller bearing operation is not obtained in the race, as is the case, for example, with roller bearing steel.
As a consequence of the high stress due to the centrifugal force and the eccentric movement of the permanent grease lubrication of the roller bearing, these known, highly stressed needle bearings are lubricated with oil, the oil being supplied to the bearing by way of a borehole system in the drive shaft.